As semicircular canal injury, benign paroxysmal positional vertigo is known, for example. In this disease, when the head is quickly moved to change its direction up and down, from side to side, or the like, rotatory vertigo occurs, where the person feels if the head spins.
Incidentally, in the vestibule, which is the organ responsible for the sense of balance, there are three semicircular canals that play an important role in maintaining the balance of the body. The three semicircular canals include the following three semicircular canals, i.e., the anterior semicircular canal, the posterior semicircular canal, and the lateral semicircular canal. They have a structure in which they are at right angles to one another.
In the vestibule, further, there is an otolith organ. The structure of the otolith organ is such that the organ has a large number of dense short hairs, and minute stones (otoliths) are placed on the end portions thereof. The shaking of such otoliths allows the gravity and linear acceleration to be perceived.
When the head is moved, the lymph in the three semicircular canals also moves, and, together with this movement, hair cells create a nervous impulse to transmit the signal to the brain. The movement of the lymph in one semicircular canal corresponding to the direction in which the head moves becomes larger than the movement in the other two semicircular canals, and the brain thus recognizes the rotation of the head.
Thus, because of the functions of the vestibule and the three semicircular canals, the brain can recognize the rotation of the head and the linear movement, as well as acceleration of the body, whereby the brain performs the operation to maintain the balance of the body.
It sometimes happens that a large number of otoliths on the otolith organ in the vestibular organ are deviated from the original position for some reason, and float inside the semicircular canals or adhere to a region inside the semicircular canals called cupula (a narrow portion in each semicircular canal, which forms a narrow path for the movement of otoliths). When the head of a person is moved in this state, otoliths extraordinarily irritate the three semicircular canals, whereby the person feels giddy.
Like this, benign paroxysmal positional vertigo occurs due to the deviation of otoliths in the vestibule, followed by entry into the three semicircular canals, thereby irritating the three semicircular canals. Therefore, once the otoliths that have entered the semicircular canals are taken out in one way or another, vertigo can be eliminated completely.
As a method for removing otoliths that have entered the semicircular canals, physiotherapy is commonly used. In this method, the patient's head is moved back and forth and from side to side to apply acceleration to otoliths floating in the semicircular canals or otoliths adhering to the cupulae, thereby removing the otoliths from the semicircular canals (see, e.g., Nonpatent Document 1). However, this method is a trial-and-error method, and has a problem in that the treatment takes a long period of time and gives physical and mental pains to the patient.